The present invention relates generally to the field of thermal barrier coatings that are used in elevated temperature applications such as gas turbine engines. In particular, this invention relates to a thermal insulating ceramic coating which has a low thermal conductivity and to the metallic articles such as turbine components, (e.g. blades and vanes) that the coatings are applied to prevent the components from overheating during high temperature operation.
Advanced gas turbine engines are continuously pursuing higher thrust and efficiency by the use of increased operating temperatures. However, the demand of increasing temperature is limited by the ability of most advanced nickel and cobalt based superalloy turbine blades and vanes to maintain their mechanical strength when exposed to the heat, oxidation, erosion and corrosion environment. Thus it is desirable to increase turbine engine operating temperatures, while decreasing the heat transfer to the metallic parts. One approach is to apply a thermal barrier coating onto the turbine blades and vanes to insulate the components from the high temperature operating environment. The ability of the thermal barrier coating to decrease the temperature to the metallic substrate depends upon the thermal conductivity of the thermal barrier coating. It is therefore desirable to develop thermal barrier coatings having low thermal conductivity to insulate effectively the thermal transfer to the components used in gas turbine engines.
Efforts have been made to lower the thermal conductivity of thermal barrier coatings by modifying the chemistry and microstructure of current 7YSZ thermal barrier coating systems as disclosed in EP0816526A2, U.S. Pat. No. 6,071,628, U.S. Pat. No. 5,846,605, U.S. Pat. No. 6,183,884B1, U.S. Pat. No. 5,792,521, U.S. Pat. No. 5,687,679, W01/63008 and U.S. Pat. No. 6,284,323B1. These approaches decreased thermal conductivity of thermal barrier coatings to various extents with the minimum reported to be about half the thermal conductivity of typical 7 wt % yttria stabilized zirconia (7YSZ).
It is a main object of this invention to decrease thermal conductivity of thermal barrier coatings providing a new ceramic material with low thermal conductivity and a method of applying such a material onto the metallic articles to form a thermal barrier coating system with increase thermal insulation capability.
Briefly, the invention provides a metallic article with a metallic substrate having a thermal barrier ceramic coating on its surface, the ceramic coating comprising a plurality of first layers of about 6 to 8 wt % yttria stabilized zirconia alternating with a plurality of second layers of about 18 to 22 wt % yttria stabilized zirconia. The alternating layers can be distinct layers or gradient layers.